The disclosed invention is generally directed to electronically steered phased array antennas, and is more particularly directed to waveguide phase shifter circuitry for controllably phase shifting waveguide propagated electromagnetic energy.
A phased array antenna is a directive antenna comprising, for example, individual radiating elements which generate an electromagnetic radiation pattern having a direction that is controlled by the relative phases of the energy radiated by the individual radiation elements. Thus, the radiation of the phased array is steered by appropriately varying the relative phases of the individual radiation elements. Such variation is provided by appropriately phase shifting the radiation emanated by each element. Such steering is sometimes referred to as beam steering or scanning.
In essence, a phased array antenna provides scanning (i.e., changing beam direction) without mechanically moving the radiation elements, in contrast to a mechanically scanned antenna wherein the radiating elements are mechanically moved. An example of a phased array antenna is a group of parallel, open-ended waveguides, where each waveguide is a radiating element.
It should be understood by persons skilled in the art that phased array antennas also include receiving antennas where the received electromagnetic energy is phase shifted to provide electronic scanning.
Background information on phased array antennas can be found in the textbook Introduction To Radar Systems, Skolnik, McGraw-Hill Book Company, 1980, 1962, Chapter 8.
Known phase shifters include structures which utilize diodes to change impedance. An example is the periodically loaded-line phase shifter discussed in the above-reference Skolnik textbook at page 289, which utilizes diodes as switching elements. Important considerations with the loaded-line phase shifter include the requirement of quarter wavelength spacing between susceptance patches which constrains the locations of the diodes, and also the attendant use of many diodes. Moreover, the loaded-line phase shifter would require a large package if adapted for use with waveguides.
Another example of a phase shifter which utilizes diodes is RADANT system, which is discussed in "RADANT: New Method of Electronic Scanning," Microwave Journal, February 1981, pp. 45-53. Important considerations with the RADANT system include the necessity of a feed antenna such as a horn, and the location of the diode grids or screens outside the waveguide.
A diode phase shifter for a waveguide is disclosed and modelled in the article entitled "Diode Phase Shifter and Model In Waveguide," Lester et al., 1987 IEEE MTT-S Digest, pages 599-602. However, that phase shifter is directed to a single diode circuit forming a transversely oriented structure, which presents implementation complications if used with waveguides.
Known phase shifters also include electromechanical phase shifters wherein circuit elements are mechanically moved. Important considerations as to electromechanical phase shifters include slower switching speeds, size, weight, and complex electromechanical driving circuitry.
Other types of known phase shifters require phase shift apparatus, for example microstrips, that are separate from the main energy propagating medium, for example coaxial cable. Important considerations with such separate phase shift apparatus include transitions, mismatching and power loss.